The present invention relates to a photoreactive agent for removing harmful materials comprising at least a photoreactive semiconductor which can decompose and remove harmful materials such as malodorants and environmental pollutants by utilizing the photocatalytic reaction of the photoreactive semiconductor.
With an increase of interest in environmental problems, there has recently been an increasing demand for not only the removal of a low concentration of industrial environmental pollutants such as industrial waste gas and waste water but also the removal of malodors and indoor pollutants in daily life. As an agent for removing a low concentration of such harmful materials, in particular, malodors in daily life, there have been generally used, for example, inorganic adsorbents obtained by compositing activated carbon, silica, alumina, a metal oxide, etc.
A removing method using such an adsorbent, however, involves various problems during its employment, for example, as follows. In proportion as harmful materials are adsorbed on the adsorbent, the adsorbability is gradually decreased. Therefore, when the practical adsorbability is lost, the adsorbent has to be renewed. Accordingly, it is necessary to ascertain the duration of effectiveness of the adsorbability.
On the other hand, a method for removing harmful materials using a photoreactive semiconductor has recently been noted. Japanese Patent Laid-Open No. 61-135669 discloses a method for decomposing sulfur compounds, malodorants by irradiating a photoreactive semiconductor such as zinc oxide with ultraviolet light. Japanese Patent Examined Publication No. 2-62297 discloses a method for removing a low concentration of nitrogen oxides by using a mixture of a titanium oxide and activated carbon. Since the decomposition of such malodorants by the photoreactive semiconductor such as a titanium oxide or zinc oxide is caused by oxidative decomposition by positive holes or radicals generated on the surface of the photoreactive semiconductor by the ultraviolet irradiation, materials decomposable by the photoreactive semiconductor are not only organic substances but also sulfides and nitrogen-containing compounds such as ammonia. Moreover, the photoreactive semiconductor itself is not consumed or deteriorated by the decomposition of the malodorants, and its capability is not basically deteriorated so long as its irradiation with ultraviolet light is continued. Thus, the above-mentioned method is markedly advantageous as compared with the case of using only an adsorbent.
The decomposing capability of such photoreactive semiconductors is improved with an increase of their chance of coming into contact with harmful materials, i.e., materials to be decomposed. Therefore, the photoreactive semiconductors are most effective when used in a powder form in which the area of reaction by the contact with the harmful materials is not decreased.
However, powder of the photoreactive semiconductor is not usable as it is in practice. Moreover, in general, the photoreactive semiconductors are not substantially able to form a self-coating film unless at least calcined. Accordingly, for handling the photoreactive semiconductors, they have to be subjected to some processing, for example, employment of a structure-forming agent capable of forming a structural material, together with the photoreactive semiconductors. Japanese Patent Laid-Open No. 3-75062 discloses a photoreactive semiconductor-supporting sheet obtained by supporting a photoreactive semiconductor by the use of a latex having a minimum film-forming temperature of 60xc2x0 C. or lower.
In general, since latices have a high film-forming capability and are easily dispersible in water, they can easily be applied. However, when the photoreactive semiconductor is mixed with the latex and supported on a sheet according to the above method, a resin contained in the latex is decomposed in itself owing to the powerful oxidative effect of the photoreactive semiconductor. When the photoreactive semiconductor is a titanium oxide or the like which has a particularly high photocatalytic activity, the photoreactive semiconductor-supporting sheet is not fit for long-term use.
In addition, when the photoreactive semiconductor is used for removing harmful materials in the air, its effective photocatalytic capability cannot be obtained because the photoreactive semiconductor surface is coated with the resin, so that direct contact of the harmful materials with the photoreactive semiconductor is remarkably inhibited.
Japanese Patent Laid-Open No. 6-315614 has proposed the following purging agents for purging pollutants from the air or water: a purging agent produced by forming photocatalyst powder composed mainly of a titanium oxide (a photoreactive semiconductor) or a mixture of a titanium oxide and activated carbon into a sheet or a panel by the use of synthetic resin powder, and a purging agent obtained by adhering the same photocatalyst powder as above to the surface of a sheet material or a panel material with an adhesive.
Since a fluororesin such as polytetrafluoroethylene is used as the synthetic resin powder, the former purging agent has a structure hardly attackable by the powerful oxidative effect of the photocatalyst. This purging agent, however, is difficult to process to a large area necessary for cleaning the air, and it involves a problem of environmental pollution due to itself because it cannot be subjected to a discarding treatment such as combustion because of the too high durability of the fluororesin.
In the purging agent obtained by adhering photocatalyst powder with an adhesive, the photocatalyst powder exhibits substantially no photocatalytic capability as in the above when buried in the adhesive, and it is poor in strength as a structural material when merely sticked to the adhesive. Thus, it is impossible to increase the amount of the photocatalyst powder in which the powder acts effectively.
Further, Japanese Patent Laid-Open No. 2-187147 discloses a denitration catalyst obtained by supporting vanadium oxide on solid-supporting paper prepared by impregnating ceramic paper with a mixture of titania sol and silica sol and firing the ceramic paper.
The ceramic paper and silica sol are not photocatalytically attacked by titania sol, and the denitration catalyst is unlikely to cause environmental pollution because of such a structure. However, although a mixed film of titania sol and silica sol is rather good in strength in a dry state, it is poor in water resistance when formed by mere drying. For removing such a defect, an after-treatment such as firing is necessary as described in the above reference, but the fired ceramic paper is poor in flexibility and hence processability.
An object of the present invention is to provide a photoreactive agent for removing harmful materials which utilizes the photocatalytic capability of a photoreactive semiconductor, is excellent in ability to remove harmful materials such as malodor, is water-resistant, is not changed in characteristics over a long period of time, and can easily be produced.
The present inventors earnestly investigated and consequently have achieved the above object with a photoreactive agent for removing harmful materials which comprises a substrate and a layer containing a photoreactive semiconductor and organic fine particles coated with inorganic fine particles which is formed on at least one side of the substrate.
Basically, the photoreactive agent for removing harmful materials of the present invention is obtained by coating or impregnating a substrate with an aqueous dispersion containing a photoreactive semiconductor and organic fine particles coated with inorganic fine particles. The organic fine particles coated with inorganic fine particles according to the present invention are fine particles obtained by coating the surfaces of organic fine particles with inorganic fine particles by the interaction between the organic fine particles and the inorganic fine particles. Therefore, they are not separated into the inorganic fine particles and the organic fine particles even by dispersion in water.
At the time of film formation by the organic fine particles coated with inorganic fine particles, organic fine particles are thermally fused together with one another through spaces among inorganic fine particles located on the surfaces of the organic fine particles, to form a matrix in a three-dimensional manner. The coating film thus formed is water-resistant and moreover the inorganic fine particles are effectively arranged between the photoreactive semiconductor and the organic fine particles substantially constituting the coating film, so that the organic fine particle component can markedly avoid the strong influence of oxidative decomposition by the photoreactive semiconductor.
More advantageously, the organic fine particles do not completely cover the inorganic fine particles in the formation of the coating film. Therefore, the coating film formed is porous because pores are formed by the inorganic fine particle component of the organic fine particles coated with the inorganic fine particles. Accordingly, the gas-adsorbing properties and the ability to remove harmful materials by light are not greatly inhibited.
The above-mentioned object has been achieved also by a photoreactive agent for removing harmful materials which comprises a substrate, a layer containing a photoreactive semiconductor and a layer containing organic fine particles coated with inorganic fine particles which layers are formed in that order on at least one side of the substrate.
In this photoreactive agent for removing harmful materials, the contact of the photoreactive semiconductor with the organic fine particle component of the organic fine particles coated with inorganic fine particles can be further reduced, so that the deterioration of the coating film over a long period of time is further suppressed. Furthermore, since the strength of coating film of the photoreactive agent for removing harmful materials is determined substantially by the layer containing the organic fine particles coated with inorganic fine particles, increasing the amount of the photoreactive semiconductor, i.e., improving the ability to remove harmful materials by light is possible without greatly deteriorating the strength of the coating film.
The above-mentioned object has been further achieved by the same photoreactive agent for removing harmful materials as above except for further comprising a layer containing a water repellent on the above-mentioned layer containing organic fine particles coated with inorganic fine particles and optionally a photoreactive semiconductor.
This photoreactive agent for removing harmful materials can have a more excellent water resistance in addition to the characteristics described above.
When the inorganic fine particle component of the organic fine particles coated with inorganic fine particles is a metal oxide, it can be prepared on the organic fine particle component prepared or in the granulation for preparing the organic fine particle component. Accordingly, the organic fine particle component and the inorganic fine particle component have a sufficient mechanical strength, so that the organic fine particles coated with inorganic fine particles are not fractured by vigorous stirring for, for example, preparing a solution. In addition, the particle sizes and the like can easily be adjusted.
Furthermore, when the inorganic fine particle component is prepared in the manner described above, a porous coating film can be formed, so that the ability to remove harmful materials by light can be improved.
The above-mentioned object has been still further achieved by a photoreactive agent for removing harmful materials which comprises a substrate, a layer containing a photoreactive semiconductor and a layer containing film-forming inorganic fine particles and a water repellent which layers are formed on at least one side of the substrate.
The film-forming inorganic fine particles can form a coating film because of their film-coating properties, and the layer containing the film-forming inorganic fine particles is porous because pores are formed by the inorganic fine particles.
As in the above, the strength of coating film of the photoreactive agent for removing harmful materials is brought about by the film-forming inorganic fine particles, whereby the amount of the photoreactive semiconductor can be increased without greatly deteriorating the strength of the coating film, and the ability to remove harmful materials by light can be improved.
In addition, water resistance can also be imparted by forming a layer containing a water repellent, as the uppermost layer of the photoreactive agent for removing harmful materials.
During the production of the photoreactive agent for removing harmful materials, the photoreactive semiconductor comes into contact with not only the film-forming inorganic fine particles but also the water repellent. Therefore, when the water repellent is oxidizable, the initial ability to remove harmful materials by light is not sufficient, but after completion of the oxidation of the water repellent on the side on which the photoreactive semiconductor is in contact with the water repellent, the ability to remove harmful materials by light is equal to that attained when the water repellent is not co-used. On the other hand, water-repellent effect is brought about by the unoxidized water repellent present on the side out of contact with the photoreactive semiconductor and hence is not lessened.
The above-mentioned object has been still further achieved by a photoreactive agent for removing harmful materials which comprises a substrate, a layer containing a photoreactive semiconductor, a layer containing film-forming inorganic fine particles and a layer containing a water repellent which layers are formed in that order on at least one side of the substrate.
In this photoreactive agent for removing harmful materials, since the above-mentioned layer containing film-forming inorganic fine particles and a water repellent is replaced by the two layers, i.e., the layer containing film-forming inorganic fine particles and the layer containing a water repellent, the water repellent does not come into contact with the photoreactive semiconductor, so that the ability to remove harmful materials by light is not changed during and after the production irrespective of the oxidation resistance of the water repellent.
In addition, since the water repellent is localized in the surface of the photoreactive agent for removing harmful materials, it can exhibit water resistance more effectively.
In the above-mentioned photoreactive agent for removing harmful materials, when a layer containing film-forming inorganic fine particles is formed between the substrate and the layer containing a photoreactive semiconductor, the substrate does not come into contact with the photoreactive semiconductor because it is isolated therefrom by the film-forming inorganic fine particles. Therefore, the deterioration of the substrate by the photoreactive semiconductor is prevented over a long period of time regardless of the oxidation resistance of the substrate, namely, the deterioration of the photoreactive agent for removing harmful materials is prevented.
When a carrier is incorporated into the layer containing the photoreactive semiconductor by supporting the photoreactive semiconductor on the carrier surface to form larger granules, the leakage and dispersion of the photoreactive semiconductor can be prevented during the production and use and moreover the inactivation of active sites on the surface of the photoreactive semiconductor can be considerably suppressed as compared with an aggregate of the photoreactive semiconductor alone.
Particularly when the aforesaid carrier is a hydrated oxide capable of releasing water owing to heat, the flame retardance of the photoreactive agent for removing harmful materials can be improved.
When a flame retardant is incorporated into the substrate, the flame retardance of the photoreactive agent for removing harmful materials can be further improved.
The constituents of the photoreactive agent for removing harmful materials of the present invention are explained below in detail.
The photoreactive agent for removing harmful materials of the present invention comprises a substrate and the following layer or combination of layers formed on at least one side of the substrate: a layer containing at least a photoreactive semiconductor and organic fine particles coated with inorganic fine particles; a combination of a layer containing at least a photoreactive semiconductor and a layer containing at least organic fine particles coated with inorganic fine particles which layers are formed in that order; a combination of the above-mentioned layer(s) and a layer containing a water repellent which is formed on the any of the above-mentioned layers containing at least organic fine particles coated with inorganic fine particles; a combination of a layer containing at least photoreactive semiconductor and a layer containing at least film-forming inorganic fine particles and a water repellent which layers are formed in that order; or a combination of a layer containing at least photoreactive semiconductor, a layer containing at least film-forming inorganic fine particles and a layer containing at least a water repellent which layers are formed in that order.
If necessary, the photoreactive agent for removing harmful materials of the present invention may further comprises a layer containing at least film-forming inorganic fine particles between the aforesaid substrate and the aforesaid layer containing at least a photoreactive semiconductor, may contain a carrier in the layer containing at least a photoreactive semiconductor, or may contain a flame retardant in the substrate.
Further, in the photoreactive agent for removing harmful materials of the present invention, the inorganic fine particle component of the above-mentioned organic fine particles coated with inorganic fine particles is a metal oxide, or the substrate is a hydrated oxide capable of releasing water owing to heat.
The photoreactive semiconductor, the most important component of the photoreactive agent for removing harmful materials of the present invention is a semiconductor which induces photocatalytic reaction and has a forbidden band width of 0.5 to 5 eV, preferably 1 to 4 eV, for example, fine titanium oxide particles, zinc oxide particles, tungsten oxide particles and cerium oxide particles. Of these oxides, titanium oxides are the most suitable for use in life spaces from the viewpoint of its structure stability, ability to remove harmful materials by light, safety in handling, etc., and are advantageously used as the photoreactive semiconductor according to the present invention.
The titanium oxides advantageously usable as the photoreactive semiconductor are industrially produced by hydrolysis of titanyl tetrachloride or titanyl sulfate or vapor phase combustion of titanyl tetrachloride. Metatitanic acid obtained by hydrolyzing titanyl sulfate is an inexpensive and excellent photoreactive semiconductor.
In addition to these production processes, there is a process for producing a titanium oxide from an organic titanate, and this process gives a photoreactive film having high uniformity and transparency.
As other titanium oxides, titanium oxides such as metatitanic acid, orthotitanic acid and hydrous titanium oxide, hydrated titanium oxide, titanium hydroxide [Ti(OH)4], hydroxyl titanium (Ti(OH)mXn, X is oxygen atom, [m+n=4], etc. may be used as the photoreactive semiconductor according to the present invention.
In the photocatalytic action of the above-exemplified titanium oxide, a reaction induced by radicals generated on the surface plays a principal role. For imparting reducing properties due to electrons more markedly, titanium oxide may be coated with metal fine particles of platinum, gold, vanadium, silver, copper, zinc, rhodium or the like. For imparting reducing properties due to positive holes more markedly, titanium oxide may be coated with a metal oxide such as ruthenium oxide.
The ability of the photoreactive semiconductor to remove harmful materials by light can be effectively attained by increasing the specific surface area of the photoreactive semiconductor to increase the number of generation sites of radicals. Furthermore, when the specific surface area is increased, the contact area per unit amount of the photoreactive semiconductor with the harmful materials is also increased. Therefore, for decomposing the harmful materials, the larger the specific surface area, the more effective the photoreactive semiconductor.
However, when the specific surface area of the photoreactive semiconductor is increased, the cohesive force of the photoreactive semiconductor itself is increased, so that the contact rate of the harmful materials with the photoreactive semiconductor is undesirably decreased. Accordingly, the specific surface area of the photoreactive semiconductor used in the present invention is preferably approximately 10-500 m2/g, more preferably approximately 100-500 m2/g. Particularly when a titanium oxide is used as the photoreactive semiconductor, the specific surface area is preferably approximately 50-400 m2/g, more preferably approximately 100-400 m2/g. The particle size of the photoreactive semiconductor is preferably approximately 3-120 nm, more preferably approximately 3-20 nm.
The content of the photoreactive semiconductor in the layer containing at least the photoreactive semiconductor and organic fine particles coated with inorganic fine particles is not remarkably related to constituents other than the photoreactive semiconductor which constitute the layer, for example, the organic fine particles coated with inorganic fine particles, and is preferably 1 to 50 g/m2, more preferably 2 to 30 g/m2.
When the content of the photoreactive semiconductor is less than 1 g/m2, the decomposing effect on harmful materials is not substantially expectable. On the other hand, when the content of the photoreactive semiconductor is more than 50 g/m2, the reach of actinic rays and the degree of contact with harmful materials are not increased as much. On the contrary, such a content undesirably causes leakage and dispersion of the photoreactive semiconductor because the photoreactive semiconductor cannot be firmly kept in the matrix of the photoreactive agent for removing harmful materials.
The larger the absolute amount of the photoreactive semiconductor becomes, the larger the decomposing effect on harmful materials tends to be expectable. Therefore, it is preferable to increase the content of the photoreactive semiconductor in a range where characteristics such as handling properties are satisfactory.
The organic fine particles coated with inorganic fine particles have a form in which the surfaces of organic fine particles are coated with inorganic fine particles. Also after the formation of a coating film, they have an archipelago structure in which the inorganic fine particle component is dispersed as micro particles in a matrix formed by the organic fine particle component.
When the photoreactive semiconductor is formed into a layer together with the organic fine particles coated with the inorganic fine particles, the inorganic fine particle component is located between the photoreactive semiconductor and the organic fine particle component, so that the organic fine particle component can markedly avoid the strong influence of oxidative decomposition by the photoreactive semiconductor.
As the inorganic fine particles, those which interact with the photoreactive semiconductor are used, so that the photoreactive semiconductor is preferentially located on the inorganic fine particles not only physically but also chemically. Therefore, the influence of the photoreactive semiconductor can be further suppressed.
On the other hand, in a coating film formed of a mere mixture of the photoreactive semiconductor, inorganic fine particles and organic fine particles, or a coating film formed of a mixture prepared by mixing inorganic fine particles and organic fine particles and then mixing the photoreactive semiconductor therewith, the contact of the photoreactive semiconductor with the organic fine particles is remarkably increased even when the inorganic fine particles are those which interact with the photoreactive semiconductor. Therefore, such coating films are much more liable to be influenced by the strong oxidative decomposition due to the photoreactive semiconductor than the coating film composed of the above-mentioned organic fine particles coated with inorganic fine particles and the photoreactive semiconductor.
As the inorganic fine particle component of the organic fine particles coated with inorganic fine particles according to the present invention, there may be exemplified smectites such as saponite, iron saponite, hectorite, sauconite, Stevensite, montmorillonite, Beidellite, etc.; micas such as vermiculite, phlogopite, sodium mica, Leacite mica, etc.; chlorites such as Clinochlore, chamosite, Sudoite, clintonite, margarite, Surite, etc.; kaolinites such as chrysotile, antigorite, kaolinite, dickite, nacrite, halloysite (7 xc3x85, 10xc3x85), etc.; and other minerals and composites, such as sepiolite, palygorskite, Fraipontite, sericite, Zeeklite(copyright), diatomaceous earth, hydrotalcite, talc, etc.; aluminum oxides such as hydrated aluminum oxide (alumina), zeolite, etc.; aluminum hydroxide; aluminum oxidesilicon oxide composites including activated clay, acid clay, aluminum silicate, etc.; hydrated silicon oxide (silica); metal-silicic acid composites such as calcium silicate, magnesium silicate, titanium silicate, etc.; and water-insoluble or difficultly water-soluble metal oxides, hydroxides, carbonates, phosphates or sulfates, such as magnesium oxide, magnesium hydroxide, magnesium carbonate, calcium phosphate, calcium carbonate, calcium oxide, barium sulfate, zirconium oxide (zirconia), zirconium carbonate, antimony oxide, iron oxide, tin oxide, zinc oxide, titanium oxide (rutile, anatase), etc.
Of these, preferable are the water-insoluble or difficultly water-soluble metal oxides including their hydrates, such as hydrated aluminum oxide, aluminum oxide, hydrated silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, antimony oxide, iron oxide, tin oxide, zinc oxide, titanium oxide, etc.; and the composite metal oxides. Particularly preferable are silicon oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide and titanium oxide.
Particles of these metal oxides are prepared by various methods such as oxidation by metal combustion, dehydrating oxidation of a metal hydroxide, hydrolytic oxidation of a metal salt, and hydrolysis or oxidation by combustion of a metal alkoxide. There is also known the sol-gel process which comprises using a solution of an organic or inorganic metal compound as a starting material, hydrolyzing and polymerizing the compound in the solution to convert the solution to a sol containing metal oxide or hydroxide fine particles dissolved therein, accelerating the reaction to convert the sol to a gel, and heating the gel to prepare a solid of oxide. This process is preferable because it permits granulation at a relatively low temperature and the (hydrated) metal oxide obtained thereby is often porous.
The average particle size of inorganic fine particle component of the organic fine particles coated with inorganic fine particles according to the present invention is preferably approximately 1-60 nm, more preferably 2-40 nm. With a decrease of the particle size of the organic fine particle component, the stability of a dispersion of, at least, the organic fine particles coated with inorganic fine particles is deteriorated or the strength of a coating film formed is deteriorated. By contrast, with an increase of the particle size of the organic fine particle component, at least the photoreactive semiconductor is undesirably localized when a coating film is formed.
On the other hand, one or more components (monomers) used for preparing the organic fine particle component of the organic fine particles coated with inorganic fine particles according to the present invention and an atomization method employed for preparing the organic fine particle component are not limited so long as the organic fine particle component is insoluble and dispersible in water or a mixed medium of water as a main dispersion medium and an organic solvent while retaining a composite form without releasing the above-mentioned inorganic fine particles from their surfaces, and the organic fine particle component has by itself an ability to form a self-coating film, at least thermally.
As the monomer(s) which constitutes the organic fine particles used in the present invention, there may be exemplified olefins such as ethylene, chloroethylene (vinyl chloride), dichloroethylene (vinylidene chloride), propylene, 2-methylpentene, etc.; dienes such as 1,2-butadiene, 1,3-butadiene, isoprene, etc.; aromatic vinyl compounds such as styrene, methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, chloromethylstyrene, methoxystyrene, butoxystyrene, acetoxystyrene, chlorostyrene, dichlorostyrene, bromostyrene, vinyltoluene, vinylpyridine, etc.; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, furfuryl (meth)acrylate, tetrahydro-furfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, 2-dimethylaminoethyl (meth)acrylate, 2-diethylaminoethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate, vinyl (meth)acrylate, allyl (meth)acrylate, glycidyl (meth)acrylate, etc.; crotonic acid esters such as methyl crotonate, ethyl crotonate, isopropyl crotonate, butyl crotonate, isobutyl crotonate, sec-butyl crotonate, tert-butyl crotonate, p-cresyl crotonate, vinyl crotonate, etc.; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, etc.; unsaturated fatty acid diesters such as dimethyl maleate, diethyl maleate, dibutyl maleate, di(2-ethylhexyl) maleate, dioctyl maleate, dimethyl fumarate, diethyl fumarate, dibutyl fumarate, di(2-ethylhexyl) fumarate, dioctyl fumarate, dimethyl itaconate, diethyl itaconate, dibutyl itaconate, di(2-ethylhexyl) itaconate, dioctyl itaconate, etc.; (meth)acrylamides such as acrylamide, cyclohexylacrylamide, phenylacrylamide, methyl(meth)acrylamide, ethyl(meth)acrylamide, butyl(meth)acrylamide, tert-butyl(meth)acrylamide, 2-methoxyethyl(meth)acrylamide, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, etc.; and vinyl ethers such as methyl vinyl ether, butyl vinyl ether, hexyl vinyl ether, methoxyethyl vinyl ether, dimethylaminoethyl vinyl ether, etc.
The polymer obtained from any of these monomers may be either a homopolymer or a copolymer. In addition to the above-exemplified monomers, there may be copolymerized any of unsaturated fatty acids such as (meth)acrylic acid, crotonic acid, etc.; aliphatic unsaturated dibasic acid monoesters such as mono-methyl maleate, monoethyl maleate, monobutyl maleate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, etc.; acrylonitriles; and methacrylonitriles.
Specific examples of the copolymer are styrene/butadiene copolymers, ethylene/vinyl acetate copolymers, vinyl chloride/vinyl acetate copolymers, ethylene/vinyl acetate/vinyl chloride copolymers, styrene/maleic anhydride copolymers, styrene/maleic acid monoalkyl ester copolymers, methacrylic acid/methacrylate copolymers, styrene/methacrylic acid/methacrylate copolymers, acrylic acid/methacrylate copolymers, styrene/acrylic acid/methacrylate copolymers, vinyl benzoate/crotonic acid copolymers, and vinyl acetate/crotonic acid/methacrylate copolymers.
There may also be exemplified copolymers in which backbone chain is a polyester, nylon or fluorocarbon polymer, and the side chain is an acrylic copolymer, styrene-based copolymer or a side chain containing a reactive atomic group such as vinyl group.
In addition, there may be used polyester resins, polycarbonate resins, polyacrylate resins, phenoxy resins, phenolic resins, butyral resins, etc.
The minimum film-forming temperature of the organic fine particles is preferably 150xc2x0 C. or lower, more preferably 120xc2x0 C. or lower. The film properties of the organic fine particles are, of course, preferably good. The term xe2x80x9cfilm propertiesxe2x80x9d used here mainly means film strength. Needless to say, the film properties have to be such that the film is free from stickiness and blocking. In the present invention, it is not preferable that pores formed by groups of particles are thermally deformed to be completely lost before film formation, so that a uniform film is formed. The reason is that when there is formed a layer containing the photoreactive semiconductor and the organic fine particles coated with inorganic fine particles, the organic fine particle component is very likely to envelop the photoreactive semiconductor and the inorganic fine particles. Therefore, ideal organic fine particles in the present invention are those which are not thermally deformed to a great degree and give a high film strength by limited contact of the particles with one another.
Although depending on the particle size of the coating organic fine particle component, the average particle size of the organic fine particle component of the organic fine particles coated with inorganic fine particles according to the present invention is preferably approximately 5-1,000 nm, more preferably 20-500 nm. With a decrease of the particle size of the organic fine particle component, the stability of a dispersion of at least the organic fine particles coated with inorganic fine particles is deteriorated, or the strength of a film formed is deteriorated. By contrast, with an increase of the particle size of the organic fine particle component, at least the photoreactive semiconductor is localyzed during film formation. Therefore, it is not preferable that the particle size of the organic fine particle component is outside the above range.
The average particle size of the organic fine particles coated with inorganic fine particles is preferably approximately 7-1,100 nm, more preferably 23-560 nm. The ratio of the particle size of the inorganic fine particle component to that of the organic fine particle component is preferably approximately 1:3 to 1:100, more preferably approximately 1:5 to 1:50. When the ratio of the particle size of the inorganic fine particle component to that of the organic fine particle component is increased, pores obtained after film formation are small, resulting in decreased contact of harmful materials with the photoreactive semiconductor. When the ratio is decreased, the film strength is deteriorated. Therefore, it is not preferable that the ratio is outside the above range.
The percentage of coverage of the organic fine particle component with the inorganic fine particle component in the organic fine particles coated with inorganic fine particles is preferably 1 to 100%, more preferably 5 to 80% when as percentage of coverage of 100%, there is taken the percentage in the case where the inorganic fine particle component is in contact with the surface of the organic fine particle component without a space for further contact of the inorganic fine particle component and without piling of inorganic fine particles. When the percentage of coverage with the inorganic fine particle component is too low, namely, the percentage of exposure of the organic fine particle component is high, the organic fine particle component tends to be deteriorated by the photoreactive semiconductor. By contrast, when the percentage of coverage with the inorganic fine particle component is too high, the fusion of organic fine particles together with one another is inhibited, resulting in a deteriorated film strength. Therefore, it is not preferable that the percentage of coverage is outside the above range. The content of the inorganic fine particle component in the organic fine particles coated with inorganic fine particles is approximately 2-80% though it cannot be unequivocally determined because it depends on the specific gravities of the organic fine particle component and the inorganic fine particle component.
The organic fine particles coated with inorganic fine particles according to the present invention may be formed, for example, by a method of forming inorganic fine particles simultaneously with the formation of organic fine particles; a method of forming organic fine particles at first, reacting an inorganic-organic interaction accelerator capable of interacting with inorganic fine particles, with the organic fine particles in the course of or after the formation of the organic fine particles, and then reacting therewith inorganic fine particles; or a method of forming at first organic fine particles so that an agent for forming inorganic fine particles may be located on the surfaces of the organic fine particles, and then forming inorganic fine particles from the agent for forming inorganic fine particles.
When granulation for preparing the inorganic fine particle component is carried out at the time of preparing the organic fine particles coated with inorganic fine particles, the above-mentioned sol-gel process may be preferentially employed.
As an example of process for producing the organic fine particles coated with inorganic fine particles according to the present invention, in the manner described above, there is a process which, as disclosed in Japanese Patent Laid-Open Nos. 59-71316 and 60-127371, comprises mixing a copolymerizable monomer with an inorganic-organic interaction accelerator (e.g. a monomer having in the molecule a polymerizable unsaturated double bond and an alkoxysilane group, or vinylsilane) and the inorganic fine particle component, and fixing the inorganic fine particle component on the surface of the organic fine particle component in the course of preparing the organic fine particle component by emulsion polymerization and granulation.
There may also be exemplified a process which comprises precipitating a silica component as inorganic fine particles on the surfaces of previously formed organic fine particles by the use of a hydrolyzable alkoxysilane non-miscible with water, such as ethyl orthosilicate, and fixing the same, as described in xe2x80x9cCollection of summaries in international forum about polymer microspheresxe2x80x9d, pp. 181-184 (1991).
Specific examples of the inorganic-organic interaction accelerator are various coupling agents including silane coupling agents such as vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, tris(2-methoxyethoxy)vinylsilane, xcex3-glycidoxypropyltrimethoxysilane, xcex3-methacryloxypropyltrimethoxysilane, xcex3-(2-aminomethyl)aminopropyltrimethoxysilane, xcex3-chloropropyltrimethoxysilane, xcex3-mercaptopropyltrimethoxysilane, xcex3-aminopropyltriethoxysilane, etc.; titanate type coupling agents such as isopropyltriisostearoyl titanate, isopropyltricumylphenyl titanate, isopropyltri-n-dodecylbenzenesulfonyl titanate, isopropyltris(dioctyl pyrophosphate) titanate, tetraisopropylbis(ditridecyl phosphite) titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, isopropyldimethacryloylisostearoyl titanate, etc.; aluminum-containing coupling agents such as (alkyl acetoacetate)aluminum diisopropylate; and zircoaluminate type coupling agents.
The content of the organic fine particles coated with inorganic fine particles in the layer containing at least the photoreactive semiconductor and the organic fine particles coated with inorganic fine particles may be a minimum amount at which the photoreactive semiconductor is not leaked out and dispersed from the photoreactive agent for removing harmful materials. That is, the content may be such that the layer containing at least the photoreactive semiconductor and the organic fine particles coated with inorganic fine particles forms a coating film and retains the practical film strength over a long period of time. Making the content of the organic fine particles coated with inorganic fine particles higher than such a content is not preferable because it improves the stability of the photoreactive agent for removing harmful materials but deteriorates the more important ability to remove harmful materials.
The mixing ratio of the organic fine particles coated with inorganic fine particles to the photoreactive semiconductor is preferably approximately 10:1 to 1:5 by weight, more preferably 5:1 to 1:3 by weight. It is preferable to increase the percentage of coverage of the organic fine particle component with the inorganic fine particle component in the organic fine particles coated with inorganic fine particles and increase the content of the photoreactive semiconductor in the mixture, so long as the strength of a coating film obtained from a dispersion of the mixture can be assured.
A small amount of a binder capable of forming a self-coating film may be co-used in the layer containing at least the photoreactive semiconductor and the organic fine particles coated with inorganic fine particles. The binder is preferably one which is soluble or stably dispersible together with at least the photoreactive semiconductor in water or a mixture of water and a solvent miscible with water, and forms a coating film on solvent removal and optional heating.
As the binder, there may be exemplified organic binders such as the above-mentioned organic fine particle component of the organic fine particles coated with inorganic fine particles, starches, natural gums, chitosan, alginic acid salts, cellulose derivatives (e.g. carboxymethyl cellulose and hydroxyethyl cellulose), poly(vinyl acetate)s, poly(vinyl alcohol)s, various synthetic acid emulsions, various latices of NBR, SBR, etc., poly(vinyl butyral) resins, polyurethane-ureas obtained from a polyvalent isocyanate and a polyvalent amine or a polyhydric alcohol, and aminoplast resins obtained by polymerization of an amino compound (e.g. a melamine/formaldehyde resin) and formaldehyde; and inorganic binders such as the film-forming inorganic fine particles described hereinafter.
The organic binders are superior to the inorganic binders in binding strength when used in the same amount as that of the inorganic amount, but they are very likely to be deteriorated by the photocatalytic action of the photoreactive semiconductor. Therefore, the inorganic binders are preferentially co-used. Moreover, the inorganic binders are preferable because basically, particles thereof are not thermally deformed during film formation, so that pores are formed among the particles.
The above-mentioned layer containing at least the photoreactive semiconductor and the organic fine particles coated with inorganic fine particles may be composed of either a single layer containing a mixture of at least the photoreactive semiconductor and the organic fine particles coated with inorganic fine particles, or a laminate of two separate layers, i.e., a layer containing at least the photoreactive semiconductor and a layer containing at least the organic fine particles coated with inorganic fine particles. In the photoreactive agent for removing harmful materials which has the layer containing at least the photoreactive semiconductor and the layer containing at least the organic fine particles coated with inorganic fine particles, the contact of the photoreactive semiconductor with the organic fine particle component of the organic fine particles coated with inorganic fine particles can be further avoided.
Unlike the single layer of the mixture with the photoreactive semiconductor, the separately laminated layer containing the organic fine particles coated with inorganic fine particles need not hold the photoreactive semiconductor therein, and it is sufficient that the organic fine particles coated with inorganic fine particles in this layer merely form a coating film. Therefore, the using amount of the organic fine particles coated with inorganic fine particles may be smaller than in the single layer of the mixture and is preferably 0.5 to 20 g/m2, more preferably 1 to 10 g/m2 irrespective of, for example, the content of the photoreactive semiconductor in the layer containing the photoreactive semiconductor.
The laminating of the separate layers makes it possible to increase the amount of the photoreactive semiconductor without greatly deteriorating the film strength, and can improve the ability to remove harmful materials by light.
In the laminating of the layer containing at least the organic fine particles coated with inorganic fine particles on the layer containing at least the photoreactive semiconductor, when it is difficult to form the layer containing the photoreactive semiconductor by using the photoreactive semiconductor alone, a binder capable of forming a self-coating film may be co-used in this layer. In this case, since the binder comes into direct contact with the photoreactive semiconductor, the binder is likely to be oxidized by the photoreactive semiconductor, or the contact of harmful materials with the photoreactive semiconductor is likely to be inhibited. Therefore, as the binder, a non-oxidizable inorganic binder capable of forming a porous film is preferable.
A layer containing a water repellent may be formed on the surface of uppermost layer of the above-mentioned photoreactive agent for removing harmful materials which comprises a substrate and a layer containing at least a photoreactive semiconductor and organic fine particles coated with inorganic fine particles which layers are formed on at least one side of the substrate, or the above-mentioned photoreactive agent for removing harmful materials which comprises a substrate, a layer containing at least a photoreactive semiconductor and a layer containing at least organic fine particles coated with inorganic fine particles which layers are formed on at least one side of the substrate, namely, the surface of the layer containing at least the organic fine particles coated with inorganic fine particles and optionally the photoreactive semiconductor.
The water repellent referred to herein is not always required to be capable of forming a coating film at least by itself, and it may be such that when water adheres to the surface of the layer containing the water repellent, water may be penetrate into other directions in at least a gaseous state. However, the surface of a coating film formed by the water repellent have to be water-repellent.
In the present invention, when the contact angle (water, 20xc2x0 C.) of a layer containing only an agent capable of imparting water repellency is 90xc2x0 or more, the layer is considered water-repellent, and the agent capable of giving the water-repellent surface is called a water repellent. The water repellent used in the present invention is preferably one which has a contact angle of 100xc2x0 or more, and preferably one which has a contact angle of 110xc2x0 or more.
As the water repellent, there may be exemplified fluorine-containing water repellents, silicone type water repellents, wax emulsion type water repellents, water repellents obtained by simultaneous use of an acrylic resin and paraffin wax, melamine type water repellents, methylolamide type water repellents, metal complex salt type water repellents, and alkylurea type water repellents. These water repellents include solvent-soluble type ones, water-dispersible type (emulsifiable type) ones, and reaction initiator (catalyst) co-use polymerization type (two-solution mixed type) ones, and any of them may be used. Of these a water repellents, the fluorine-containing water repellents and the silicone type water repellents are preferable from the viewpoint of ease of imparting water repellency, the water repellency, their weather resistance, etc.
As the fluorine-containing water repellents, there may be used fluorine-containing compounds generally used as water and oil repellents. Specific examples of the fluorine-containing compounds are perfluoro aliphatic compounds such as polytetrafluoroethylenes, tetrafluoroethylene-hexafluoropropylene copolymers, etc.; polyperfluoroalkyl acrylates or methacrylates such as polypentadecafluorooctyl (meth)acrylates, polytrifluoroethyl (meth)acrylates, etc.; perfluorourethane resins obtained by the reaction of a polyfluoroalcohol such as pentadecafluorooctanol or pentadecafluorodecanol with a polyisocyanate such as hexamethylene diisocyanate or toluene diisocyanate; and the compounds obtained by random copolymerization of terephthalic acid, a saturated polybasic acid, a saturated polyhydric alcohol and a reaction product of a polyfluoroalcohol with a polyisocyanate, which are disclosed in Japanese Patent Laid-Open No. 62-205181.
As the silicone type water repellents, there may be used silicone type compounds generally used as water repellents, softeners, mold release agents or lubricants. As the silicone type compounds, there may be exemplified dimethyl polysiloxanes, methylhydrogen polysiloxanes, methylphenyl polysiloxanes, dimethylsiloxane-methylphenylsiloxane copolymers, block copolymers of a dimethylsiloxane or a methylphenylsiloxane and a monomer other than silicones, polysiloxane compounds obtained by modifying a dimethyl polysiloxane by introducing one or more amino groups, epoxy groups, hydroxyl groups, polyether groups or the like into the end of the molecule or the side chains, and alkyl (meth)acrylate (partially) substituted derivatives obtained by substitution of the alkyl group by a dimethyl polysiloxane or a methylphenyl polysiloxane.
The water repellents including above-exemplified fluorine-containing water repellents and silicone type water repellents may be used singly or as a mixture or laminate thereof. The water repellents are used in the form of an emulsion in water or a solution in a solvent.
In addition to the water repellent and the solvent (dispersion medium), inorganic or organic binders, surfactants, crosslinking agents, antistatic agents, softeners, hardening and finishing agents, coloring agents, etc. may be incorporated into the layer containing the water repellent.
The water resistance required of the photoreactive agent for removing harmful materials of the present invention is such that in both of the following cases, even if water penetrates into the layer containing at least the photoreactive semiconductor, the penetration does not cause a gradual decrease of the film strength and hence peeling of the layer: when dirt on the surface of said removing agent is removed with a wet cloth or the like, namely, when the surface is rubbed while being brought into contact with water even for a short period of time; and when said removing agent is used under conditions of high temperature and humidity for a long period of time, namely, when the removing agent is in contact with water vapor for a long period of time though its surface is not rubbed.
The resistance of the laminate to rubbing with a dirt-removing means such as a cloth cannot be measured according to the same criterion as in the case of the resistance of the laminate to water penetration. Even if the amount of the water repellent is increased, at least the water repellency (the contact angle of water) has a definite upper limit. On the other hand, even if the mechanical film thickness can be improved by the use of the water repellent, the film strength does not reach the upper limit at all at a minimum amount of the water repellent which gives the upper limit value of the water repellency. Therefore, in the present invention, the amount of the water repellent used may be set for its minimum amount at which the contact angle of water reaches the upper limit.
Although the upper limit value of the contact angle varies depending on the kind of the water repellent, the amount of the water repellent which gives this upper limit value is substantially constant regardless of the kind of the water repellent. Although the amount of the water repellent used in the present invention is varied depending on whether the uppermost layer of the photoreactive agent for removing harmful materials of the present invention contains a photoreactive semiconductor, the amount is preferably 0.02 to 10 g/m2 in general and the most suitable amount is 0.1 to 2 g/m2.
As in the above-mentioned photoreactive agent for removing harmful materials of the present invention which has the uppermost layer containing a water repellent, water resistance due to a water-repellent surface can be attained also in a photoreactive agent for removing harmful materials which comprises a substrate, a layer containing at least a photoreactive semiconductor and a layer containing at least film-forming inorganic fine particles and a water repellent which layers are formed in that order on at least one side of the substrate.
That is, the film-forming inorganic fine particles can form a film because of their film-forming properties, and the same effect as that of the above-mentioned organic fine particles coated with inorganic fine particles can be brought about by the film-forming inorganic fine particles. Pores are formed in the layer containing the film-forming inorganic fine particles because of the fineness of these particles, so that the layer has at least gas permeability.
The film-forming inorganic fine particles used in the present invention are water-insoluble inorganic fine particles which are stably or almost stably dispersible in a solvent composed mainly of water and are at least capable of forming a film. The term xe2x80x9cfilm-formingxe2x80x9d used herein means that when the inorganic fine particles used in the present invention are dispersed in a suitable dispersion medium, applied on the substrate used in the present invention or the like and then dried, the resulting film is not peeled off and retain continuity even when a considerable external force is applied thereto. Therefore, if the film is cracked or returns to a powdery state owing to drying for a long period of time and mere light touch of a finger or the like to the surface of the formed film transfers a considerable amount of a powdery material, it is judged in the present invention that the inorganic fine particles have no film-forming properties.
As the film-forming inorganic fine particles used in the present invention, there may be exemplified fine particles of natural clays and minerals such as smectites (e.g. saponite, iron saponite, hectorite and montmorillonite), vermiculites, kaolinites-serpentines [e.g. kaolinite and halloysite (10)], sepiolite, etc.; colloidal silica; colloidal alumina; modified products thereof; and synthetic inorganic high-molecular weight compounds.
In the present specification, the term xe2x80x9cmodifiedxe2x80x9d in the aforesaid modified products means the development of characteristics inherent in the original minerals or the impartment of other characteristics to the original minerals, which is carried out, for example, by following method: impurities or a specific atomic group is removed from the natural minerals; a desired element in elements constituting the natural minerals is replaced by another element by treatment according to a suitable method; or physical properties of the mineral surface are modified by chemical treatment with another compound. Specific examples of the modified products referred to herein are Na-montmorillonite obtained by ion exchange carried out by treating Ca-montmorillonite with sodium carbonate or the like in the presence of water, and modified products obtained by treatment with, for example, a cationic surfactant and/or a nonionic surfactant.
The synthetic inorganic high-molecular weight compounds refer to compounds which are obtained by synthesis so as to have the same composition as that of a natural mineral or by replacing one or more element of the same composition as that of a natural mineral to give characteristics equal or superior to that of the natural mineral, and are obtained by reacting two or more compounds with each other. As the synthetic inorganic high-molecular weight compounds, there may be exemplified so-called fluoro-mica having an elemental composition obtained by replacing the hydroxyl group of the structure of natural mica by fluorine, and synthetic smectite.
Specific examples of fluoro-mica are fluorophlogopite [KMg3(AlSi3O10)F2], fluoro-mica tetrasilicide [KMg2.5(Si4O10)F2] and Taeniolite [KMg2Li(Si4O10)F2].
The film-forming inorganic fine particles are preferably those which are in colloidal state in at least a coating fluid. Therefore, particularly when a natural material is used as the film-forming inorganic fine particles, it is necessary to grind the natural material into fine particles and remove non-colloidal substances previously by a suitable method. When the viscosity of a coating fluid prepared from the film-forming inorganic fine particles is very high, a dispersant (a viscosity depressant) such as a hexametaphosphate may be co-used. Of such film-forming inorganic fine particles, examples of film-forming inorganic fine particles preferably used in the present invention are colloidal alumina and colloidal silica which are excellent not only in ease of fluid preparation (i.e. dispersibility in preparing a dispersion of the film-forming inorganic fine particles) and characteristics of a coating fluid (e.g. coating properties) but also in film strength such as the mechanical strength and weather resistance of the film.
Colloidal alumina is amorphous or pseudoboehmite (including boehmite in wide sense)-like alumina hydrate in a colloidal state dispersed in a form of feather, fiber or disc.
As commercially available colloidal alumina, there may be exemplified Aluminasol-10, Aluminasol-20, Aluminaclearsol, Aluminasol-SH5, Aluminasol-CSA55, Aluminasol-SV102, Aluminasol-SB52 manufactured by Kawaken Fine Chemical K.K.; Cataloid-AS (AS-1, AS-2 and AS-3) and Cataloid-AP manufactured by Shokubai Kasei Kogyo K.K.; and Aluminasol-100, Aluminasol-200 and Aluminasol-520 manufactured by Nissan Kagaku Kogyo K.K.
Colloidal silica is noncrystalline silicon dioxide in a colloidal state having a particle size of approximately 4-100 nm. In general, colloidal silica refers to silicon oxide suspended in water as a hydrate though it exists also in the form of a non-aqueous suspension or fine powder. As to a production process, colloidal silica is obtained by adding a silicon tetrahalide to water or removing ions such as alkali ions while gradually neutralizing an aqueous alkali silicate solution. Such colloidal silica includes not only unmodified colloidal silca conventionally generally used but also modified colloidal silica possessing changed ionicity of particles and changed behavior thereof toward pH change which is obtained by modifying the silca surface with ions of ammonia, calcium, magnesium, alumina or the like or a compound thereof.
As commercially available colloidal silica, there may be exemplified Adelite AT-20, Adelite AT-20N, Adelite AT-30A, Adelite AT-20Q, etc. manufactured by Asahi Denka Co., Ltd.; Cataloid SA, Cataloid SN, Cataloid S-30L, Cataloid SI-30, Cataloid SI-50, Cataloid SI-350, Cataloid SI-45P, etc. manufactured by Shokubai Kasei Kogyo K.K.; Ludox LS, Ludox HS-30, Ludox SM-30, Ludox AS, Ludox AM, etc. manufactured by E.I. du Pont de Nemours and Co.; Snowtex-20, Snowtex-N, Snowtex-O, Snowtex-S, Snowtex-SS, Snowtex-20L, Snowtex-XL, Snowtex-AK, Snowtex-UP, etc. manufactured by Nissan Kagaku Kogyo K.K.; and Silicadol-20, Silicadol-20A, Silicadol-20P, etc. manufactured by Nihon Kagaku Kogyo K.K.
The amount of the film-forming inorganic fine particles in the layer containing at least the film-forming inorganic fine particles and a water repellent according to the present invention is preferably 1 to 100 g/m2.
In general, with an increase of the amount of the film-forming inorganic fine particles, the powder-dropping properties of the photoreactive semiconductor in the layer under the film-forming inorganic fine particles is improved but the ability to remove harmful materials by light is deteriorated. When the amount of the film-forming inorganic fine particles is less than 1 g/m2, the powder-dropping properties are substantially the same as that before coating with the film-forming inorganic fine particles. To improve the powder-dropping properties, an amount of the film-forming inorganic fine particles of 100 g/m2 is sufficient. A larger amount of the film-forming inorganic fine particles merely deteriorates the ability to remove harmful materials by light and hence is not preferable. The amount of the film-forming inorganic fine particles are more preferably 2 to 50 g/m2, most preferably 5 to40 g/m2.
As the water repellent used in the layer containing at least the film-forming inorganic fine particles and the water repellent, all of the above-exemplified ones may be used. On the other hand, although the amount of the water repellent is varied depending on the amount of the film-forming inorganic fine particles mixed and the kind thereof, it is preferably 0.05 to 10 g/m2 in general and the most suitable amount is 0.2 to 3 g/m2.
To form the layer containing at least the film-forming inorganic fine particles and the water repellent, it is sufficient that the layer containing at least a photoreactive semiconductor is coated or impregnated with a coating fluid containing at least the film-forming inorganic fine particles and the water repellent. It is preferable that the coating or impregnation has no undesirable influence such as dissolution on the layer containing at least a photoreactive semiconductor and that the layer formation is carried out at as low a solid content of the coating fluid as possible so long as the coating conditions such as drying are satisfied.
The above-mentioned layer containing at least film-forming inorganic fine particles and a water repellent may be a laminate of two separate layers, i.e., a layer containing at least film-forming inorganic fine particles and a layer containing at least a water repellent. In this case, the water repellent can be localized on the surface of the photoreactive agent for removing harmful materials, so that more effective exhibition of the water resistance is possible.
Also in the case of the laminate of the layer containing at least film-forming inorganic fine particles and the layer containing at least a water repellent, there may be used the same film-forming inorganic fine particles and water repellent as used for forming the above-mentioned layer containing at least film-forming inorganic fine particles and a water repellent.
In the case of the laminate of the layer containing at least film-forming inorganic fine particles and the layer containing at least a water repellent, the content of the film-forming inorganic fine particles may be the same as in the above-mentioned mixed layer of film-forming inorganic fine particles and a water repellent from the viewpoint of the film strength and is preferably 1 to 100 g/m2. In the layer containing a water repellent, the content of the water repellent is preferably 0.05 to 8 g/m2 and the most suitable content is 0.2 to 2 g/m2.
In the above-mentioned photoreactive agent for removing harmful materials, a layer containing at least film-forming inorganic fine particles may be formed between the substrate and the layer containing at least a photoreactive semiconductor because this formation can prevent the deterioration of the substrate by the photoreactive semiconductor over a long period of time even when the substrate is oxidizable. In this layer containing at least film-forming inorganic fine particles, the same film-forming inorganic fine particles as above may be used.
In this layer containing film-forming inorganic fine particles, there may be used, together with the film-forming inorganic fine particles, clay, kaolin, talc, calcium carbonate, sericite, barium sulfate, alumina, silica, magnesium carbonate, aluminum hydroxide, titanium oxide having no photocatalytic capability, and inorganic pigments having no film-forming properties, such as zinc oxide.
The thickness of the layer containing at least film-forming inorganic fine particles which is formed between the substrate and the layer containing at least a photoreactive semiconductor may be such that at least the oxidative effect of the photoreactive semiconductor is not exercised on the substrate and that a continuous coating film can be formed. The thickness is preferably 0.5 xcexcm or more, more preferably 2 to 10 xcexcm.
In the layer containing at least a photoreactive semiconductor, a carrier may be co-used in addition to organic fine particles coated with inorganic fine particles, and film-forming inorganic fine particles.
In the formation of the layer containing at least a photoreactive semiconductor, when the photoreactive semiconductor is supported on the surface of a carrier to form larger granules before mixing the photoreactive semiconductor with other components which constitute said layer, the photoreactive semiconductor becomes easy to hold in a matrix composed of the other layer-forming components. Therefore, the leakage and dispersion of the photoreactive semiconductor can be prevented during the production and use and moreover the inactivation of active sites on the surface of the photoreactive semiconductor can be considerably suppressed as compared with an aggregate of the photoreactive semiconductor alone.
Specific examples of the carrier used in the present invention are silicon oxide (silica), aluminum oxide (alumina), zirconium oxide (zirconia), magnesium oxide (magnesia), aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, calcium hydroxide, activated clay, zeolite, sepiolite, halloysite, hydroapatite, zinc oxide, silica-alumina composite, silica-zinc oxide composite, silica-magnesia composite, zinc oxide-magnesia composite, silica-alumina-zinc oxide composite, silica-alumina-magnesia composite, and activated carbons prepared from various materials such as wood chips and coconut husks.
When there is used a carrier having gas adsorbability in itself, such as activated clay, zeolite, sepiolite and activated carbon among the above-exemplified carriers, the ability to remove harmful materials without light irradiation is also improved. In the case of this gas adsorbability, the gas adsorption is physical adsorption and is in thermal equilibrium. Therefore, when the temperature of the carrier is raised by light irradiation, harmful materials adsorbed on the carrier without light irradiation are released and at the same time, decomposed by the photoreactive semiconductor supported on the carrier. Of such carriers having gas adsorbability, there are carriers which preferentially adsorb a specific compound or either an acidic substance or a basic substance. Therefore, it is preferable to select the most suitable carrier from the above-exemplified carriers, depending on use conditions. If necessary, the carriers are preferably used in combination.
The flame retardance of the photoreactive agent for removing harmful materials can be improved by using as the carrier a hydrated oxide capable of releasing water owing to heat, such as aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, calcium hydroxide or the like.
The specific surface area of the carrier used in the present invention is preferably approximately 50-2,000 m2/g. When activated carbon is used, its specific surface area is preferably approximately 500-1,500 m2/g.
On the other hand, for the purpose of the present invention, the particle size of the carrier is preferably large to a certain extent, namely, at least about 10 times as large as that of the photoreactive semiconductor co-used. The preferable particle size of the carrier used in the present invention is 100 nm to 50 xcexcm. In particular, the preferable particle size of activated carbon is 50 nm to 10 xcexcm. The carrier may be used either in the form of granules or in the form of pellets or tablets prepared by molding the granules.
The content of the carrier in the photoreactive agent for removing harmful materials of the present invention is determined by the mixing ratio of the photoreactive semiconductor to the carrier. That is, the mixing ratio of the photoreactive semiconductor to the carrier is preferably 1:30 to 10:1, more preferably approximately 1:10 to 5:1. When the mixing ratio of the photoreactive semiconductor to the carrier is too high in the case where the absolute amount of the photoreactive semiconductor is definite, the content of the carrier in the photoreactive agent for removing harmful materials becomes too high, so that it becomes difficult to hold the photoreactive semiconductor and the carrier in the matrix of the photoreactive agent for removing harmful materials. When the mixing ratio is too low, the effect of co-use of the carrier is substantially not obtainable.
It is not necessary that the carrier should be only that supporting the photoreactive semiconductor. There may be used a carrier supporting the photoreactive semiconductor and a carrier supporting no photoreactive semiconductor, in combination or separately.
Lastly, there are explained below the substrate on which the above-mentioned layer containing at least a photoreactive semiconductor is to be formed and a method for forming the layer(s) on the substrate.
As the substrate used in the present invention, there may be exemplified paper, cloth, nonwoven fabric, wood, plywood, concrete panels, wall materials, gypsum, plastics films or boards of a poly(vinyl chloride), polyester or the like, steel plates, iron plates, aluminum plates, tin plates, glass plates, and composites and (bonded) laminates thereof.
Of these, paper composed mainly of vegetable fiber and nonwoven fabric composed mainly of synthetic resin (fiber) are preferable as the substrate used in the present invention. These substrates may be used not only in a flat form but also in a galvanized panel form or in a composite form thereof (e.g. corrugated structure or honeycomb structure).
As the vegetable fiber used as a material for the substrate used in the present invention, there may be used kraft pulps obtained from softwood or hardwood; chemical pulp such as sulfite pulp, alkali pulp, etc.; wood fibers such as semichemical pulp, semimechanical pulp, mechanical pulp, etc.; vegetable non-wood fibers such as Broussonetia kazinoki, Edgeworthia papyrifera, straw, kenaf, bamboo, linter, bagasse, esparto, etc.; regenerated fibers such as rayon, etc.; processed fibers of natural materials, such as cellulose derivative fibers, etc.
In addition, as the vegetable fiber used as a material for the substrate used in the present invention, there may be used inorganic-material-supporting fiber obtained by reacting the vegetable fiber with a water-soluble inorganic material before its formation into a sheet and then making the inorganic material water-insoluble. As to a method for supporting the water-soluble inorganic material and making the same water-insoluble, a hydrophilic fiber material is impregnated with an aqueous solution containing a water-soluble compound capable of reacting with a specific gas of aqueous solution to become water-insoluble, after which the inorganic material is brought into contact with a gas or an aqueous solution, which makes the inorganic material water-insoluble, whereby the water-insoluble inorganic material can be supported inside the fiber material.
As the synthetic resin fiber, there may be exemplified thermoplastic synthetic resin fibers of olefin resins (e.g. polyethylenes and polypropylenes), polyester type resins (e.g. Dacron), poly(vinyl acetate)s, ethylene-vinyl acetate copolymer resins, polyamide resins (e.g. nylons), polyacrylonitrile resins (e.g. Acrylan, Orlon, Dynel and Verel), poly(vinyl chloride)s, poly(vinylidene chloride)s, polystyrenes, poly(vinyl ether)s, poly(vinyl ketone)s, polyethers, poly(vinyl alcohol)s, diene type resins, polyurethane resins, etc.; thermosetting resins such as phenolic resins, furan resins, urea resins, melamine resins, aniline resins, unsaturated polyester resins, alkyd resins, epoxy resins, etc.; silicone resins; fluoro-resins; metal fiber of stainless steel, etc.; and various glass fibers. In the present example, the above-exemplified fibers may be used singly or in combination.
When the photoreactive agent for removing harmful materials of the present invention is used for removing harmful materials in a life space by its use in a wall material, ceiling material, wall paper, curtain or the like, at least the substrate used in the photoreactive agent for removing harmful materials is also preferably flame-retardant.
As fiber capable of imparting flame retardance, there may be exemplified halogen-containing fiber and aramid fiber, whose molecules themselves are flame-retardant; inorganic fibers which are intrinsically non-combustible, such as metal fiber, ceramic fiber, rock wool fiber, glass fiber, alumina fiber, zirconia fiber, silicon nitride fiber, silicon carbide fiber, carbon fiber, etc.; and fibers obtained by chemically or physically incorporating a flame retardant into generally used fiber. There may also be used a product obtained by treating a substrate made of generally used fiber with a flame retardant.
Of such substrates, those preferably used from the viewpoint of processability and material cost are substrates made of fiber obtained by chemically or physically incorporating generally used fiber with a well-known flame retardant such as any of water-soluble inorganic salts (e.g. NH4Br, NH4VO3, Na3VO4, (NH4)2MoO4 and Na2MoO4.2H2O), phosphorus- and nitrogen-containing derivatives (ethylenimine phosphate, guanidine phosphate and phosphorylphosphoramide), the phosphorus-containing halide type flame retardants disclosed in U.S. Pat. Nos. 2,725,311 and 3,087,836, and the antimony trioxidehalogen type flame retardants disclosed in U.S. Pat. No. 3,300,426 and Japanese Patent Examined Publication No. 48-35604; and the substrates treated with a flame retardant.
Anti-flaming or antiflaming agents for organic polymers are described in detail in J. W. Lyons xe2x80x9cThe Chemistry and Uses of Fire Retardantsxe2x80x9d (John Willey) 1970. The techniques described therein may be applied.
As fiber which constitutes the nonwoven fabric used as the substrate used in the present invention, activated-carbon fiber is also suitable. The activated-carbon fiber has an adsorption rate 100 to 1,000 times as high as that of common powdery activated carbon and has an adsorption per unit amount which is about 10 times as large as that of the latter. Since the activated-carbon fiber is formed by calcining starting fiber, it is intrinsically non-combustible and hence is advantageously used also for imparting flame retardance to photoreactive agent for removing harmful materials.
In processing the above-exemplified vegetable fiber material into the substrate used in the present invention, there may be added various additives such as sizing agents (e.g. rosin, its modified products, emulsions of a maleic anhydride-based synthetic resin or a styrene/acrylate synthetic resin, alkylketene dimers, and alkenylsuccinic anhydrides), strength improvers and binders [e.g. starch, its modified products, carboxymethyl cellulose, poly(vinyl alcohol)s, poly(ethylene oxide)s, polyethylenimines, polyacrylamides, polyamidoepichlorohydrins, various emulsions (including latices), urea-formaldehyde resins and melamine-formaldehyde resins], yield improvers, surfactants, defoaming agents, dyes, fluorescent whitening agents, antioxidants, slime-controlling agents, etc.
For producing the substrate, there may be used a cylinder paper machine, Foordrinier paper machine, Yankee paper machine, twin-wire paper machine, and combination paper machines such as hybrid former top former.
The nonwoven fabric used as the substrate used in the present invention may be produced, for example, by a wet process comprising suspending the above-exemplified synthetic resin fiber in water and forming the suspension into a sheet by a paper making method; a so-called dry process such as resin bonding comprising bonding of a resin, needle punching utilizing crossing by means of a needle, stitch bonding comprising knitting out of yarn, and thermal bonding comprising bonding by heat; a water-flow entangling process comprising entangling fibers with one another by jetting high-pressure water through a nozzle; spun bonding comprising forming a sheet with direct spinning; or a melt blow process comprising forming a sheet while forming very fine fibers by applying the principle of atomization at the time of direct spinning.
Since the nonwoven fabric is subjected to aqueous treatment in the present invention, it has to possess a water-wettability to a certain extent and hence is preferably that obtained from a web prepared from hydrophilic fiber. From the viewpoint of sheet strength, the nonwoven fabric is preferably processed by spun bonding or a spun lace process.
Each of the photoreactive agents for removing harmful materials which have been explained above [i.e., the photoreactive agent for removing harmful materials which has a layer containing at least a photoreactive semiconductor and organic fine particles coated with inorganic fine particles; the photoreactive agent for removing harmful materials which has a layer containing at least a photoreactive semiconductor and a layer containing at least organic fine particles coated with inorganic fine particles which layers are formed in that order; the same photoreactive agent for removing harmful materials as above except for further having a layer containing a water repellent, on at least the above-mentioned layer containing organic fine particles coated with inorganic fine particles; the photoreactive agent for removing harmful materials which has a layer containing at least a photoreactive semiconductor and a layer containing at least film-forming inorganic fine particles and a water repellent which layers are formed in that order; the photoreactive agent for removing harmful materials which has a layer containing at least a photoreactive semiconductor, a layer containing at least film-forming inorganic fine particles, and a layer containing at least a water repellent which layers are formed in that order; the same photoreactive agent for removing harmful materials as above except for further having a layer containing at least film-forming inorganic fine particles, between a substrate and the layer containing at least a photoreactive semiconductor] comprises the above-mentioned substrate and the layer(s) formed on at least one side of the substrate, and is obtained by coating or impregnating at least one side of a previously prepared substrate with one or more aqueous dispersions containing layer-forming components including a photoreactive semiconductor, and drying the thus treated substrate.
As a method for the coating or impregnation of the substrate with a coating fluid for layer formation according to the present invention, there are exemplified a method of impregnating the substrate with the coating fluid by means of a conventional size press, a gate roll size press, a film transfer type size press or the like; a method of coating the substrate with the coating fluid and optionally a small amount of a suitable binder by the same procedure as a conventional coating procedure, by means of a coater such as a roll coater, rod (bar) coater, blade coater, spray coater, air doctor (knife) coater, curtain coater or the like. Particularly in the impregnation method, the substrate may be previously wetted.
In the coating with the coating fluid for layer formation, when the substrate surface is poor in water-wettability, it is preferable to incorporate a suitable surfactant into the coating fluid or improve the water-wettability of the substrate surface by a physical or chemical treatment such as corona treatment, glow discharge treatment, plasma treatment, electron radiation treatment, far-ultraviolet irradiation treatment, ozone treatment, treatment with a surfactant, or the like.
In the present invention, a product obtained in the following process is also regarded as a photoreactive agent for removing harmful materials which has one or more layers on at least one side of a substrate: from one or more layer-forming components and one or more substrate-forming components in a layer which comes into contact with the substrate of a photoreactive agent for removing harmful materials which is to be produced, for example, a layer containing at least a photoreactive semiconductor and organic fine particles coated with inorganic fine particles, the substrate is prepared while supporting the layer-forming component(s) such as a photoreactive semiconductor on the surface of the substrate-forming component(s).
The substrate-forming component referred to herein is a component necessary for keeping the shape of a photoreactive agent for removing harmful materials which is obtained by forming an aqueous dispersion of aggregates into a sheet. The substrate-forming component is preferably fibrous. As a material for this fiber, a thermoplastic resin is preferable from the viewpoint of substrate-forming properties and post-processability. There may be used the above-exemplified thermoplastic fibers which constitute the nonwoven fabric preferably used as the substrate used in the present invention.
As to a process for producing such a photoreactive agent for removing harmful materials, it may be produced from the substrate-forming component(s) and layer-forming component(s) by basically the same process as the above production process of the substrate.
Of the photoreactive agents for removing harmful materials of the present invention, those substantially comprising a substrate and two or more layers laminated thereon [e.g. the photoreactive agent for removing harmful materials which has a layer containing at least a photoreactive semiconductor and a layer containing at least organic fine particles coated with inorganic fine particles which are formed in that order] may be obtained by forming a lowermost layer on the substrate by the above-mentioned integral-sheet formation process, and laminating upper layer(s) thereon by coating or impregnation.
In the case of the photoreactive agents for removing harmful materials of the present invention, an undercoating layer or an intermediate layer may, if desired, be laminated in the formation of each layer in order to improve the adhesive properties, etc. When the photoreactive agent for removing harmful materials of the present invention is used by joining one side thereof to another substrate, an objective equipment or the like or feeding only one side thereof with a gas containing an objective substance to be decomposed, at least a layer containing a photoreactive semiconductor and optionally other layers may be formed only on one side of the substrate used in the present invention.
In addition, when a layer containing a photoreactive semiconductor and optionally other layers are formed on each side of the substrate, the combination of these layers and the kind and content of component(s) contained in each layer on one side may be different from those on the other side.
According to the present invention, there can be provided a photoreactive agent for removing harmful materials which utilizes the photocatalytic capability of a photoreactive semiconductor, is excellent in ability to remove harmful materials such as malodor, can hold the photoreactive semiconductor excellently, can be given water resistance and the like if necessary, and can easily be produced.
The photoreactive agent for removing harmful materials can be utilized in the following by making the most suitable its substrate, a combination of layers formed thereon and the kind and content of component(s) contained in each layer: articles in life spaces such as clothing, curtains, blinds, electric appliances, illuminators, walls, doors, ceilings, floors, table cloths, furniture, and the trims of automobiles, trains, airplanes and the like; filters of air conditioners and air cleaners; and the exteriors and surfaces of structures such as erections (e.g. houses and buildings), utility poles, signals, roads, roadside zones, bridges, etc.